1. Field of the Invention
The present invention relates to a device for ventilating and draining the middle ear cavity and, more particularly, to a permanent prosthetic for maintaining patency of the eustachian tube passageway.
2. Description of the Prior Art
The eustachian tube passageway extends from the pharyngeal orifice to its tympanic orifice in the middle ear cavity. The tube consists of an anteromedial cartilaginous two-thirds and a posterolateral bony one-third. The bony portion is also referred to as the protympanum to emphasize that the bony tube is essentially an extension of the tympanic cavity. The length of the tube passageway varies from 31-38 mm, with the protympanum being about 13-14 mm in length. The end portions of the lumen are funnel shaped with the narrow, connecting isthmus measuring about 1 mm wide and 2 mm high.
Functions which have been attributed to the eustachian tube passageway include ventilation and drainage of the middle ear cavity and protection of the cavity from pathology, primarily infection, ascending from the nasal pharynx. Ventilation of the middle ear cavity is important among other reasons to maintain equilibrium with external air pressure across the tympanic membrane. Air enters the middle ear cavity when the passageway opens under normal physiological conditions. The passageway thereby permits adjustment of the air pressure in the middle ear cavity for external pressure changes. The passageway operates in a similar fashion when exposed to pressure changes that occur within the head with respiration, sneezing, speech and other similar conditions. Drainage of the middle ear cavity through the eustachian tube passageway may occur to remove fluids produced in the cavity due to, for example, allergies or infections.
Under certain conditions the eustachian tube passageway or lumen will constrict or become totally obstructed. As a result, the performance of the above-described functions will be inhibited or cease. It then becomes desirable to physically induce the performance of these functions. In addition, the absence of these functions may interfere with the treatment of related ear functions. One of the primary causes of tympanoplasty failure, for example, is the inadequate functioning of the eustachian tube passageway.
Various methods have been devised for restoring ventilation and drainage of the middle ear cavity. Drugs and radiotherapy have been used to directly restore patency of the eustachian tube passageway. For cases in which these methods are unsuccessful, various surgical procedures and implants have been employed.
One of the simpler surgical procedures involves the implantation of a transtympanic ventilation tube. U.S. Pat. No. 3,807,409, issued to Paparella et al. on Apr. 30, 1974 discloses a ventilation tube useful for this purpose. The Paparella et al. device and similar structures are inserted by making an incision in the tympanic membrane or eardrum and placing the ventilation tube therein. These devices, however, are susceptible to being spontaneously extruded into the ear canal after a period of time. Further, the devices while in place render the middle ear cavity vulnerable to infection. The mere existence of a tympanic membrane perforation may also result in problems, although the membrane will usually heal uneventfully after removal or extrusion of the ventilation tube. In general, the use of a transtympanic ventilation tube, though simple and effective for short periods of time, is not suited for use as a permanent implant.
A comparable procedure intended as a permanent measure is described in the Archives of Otolaryngology, p. 315, Vol. 91, April, 1970. In an article entitled "Permanent Middle Ear Aeration", written by Herbert Silverstein, there is described a method for inserting a permanent pressure-equalizing tube for the middle ear. The device comprises a flanged silicone rubber tube having a length of 15 mm, an inside diameter of 1.5 mm, and a flange diameter of 2.5 mm. The tube is inserted through a hole which is drilled in the bony external canal and thereby spans from the middle ear cavity to the outer ear. The disclosed procedure thus includes the disadvantages of requiring a hole to be drilled to provide a location of the tube and of exposing the middle ear to infection.
In "Tympanomaxillary Shunt, A New Method of Middle Ear Ventilation", written by Drs. Drettner and Ekball, in the Archives of Otolaryngology, p. 30, Vol. 90, August, 1969, there is disclosed a procedure for providing a permanent communication between the middle ear cavity and the maxillary sinus. The article concedes, however, that the risk of an ascending infection from the maxillary sinus to the middle ear can not be eliminated and that patients with a history of recurrent sinusitis must be considered unsuitable for this operation. In addition, the procedure is extremely complicated, is not suitable for children, and does not provide a conduit which can serve as an effective drain for the middle ear cavity. An alternative procedure is disclosed by Drs. Lapidot and Kapila in "Experimental Construction of a `New` Eustachian Tube" appearing in the Archives of Otolaryngology, p. 490, Vol. 86, November, 1967. A conduit less than about 2 inches in length is inserted by a somewhat complicated surgical procedure to span from the middle ear to the oral cavity.
One procedure involves the insertion of a plastic tube within a blocked eustachian tube passageway. This procedure is described in "Therapy of the Eustachian Tube" by Zollner in the Archives of Otolaryngology, p. 394, Vol. 78, September, 1963. The tube is maintained in place by a double-bended end which lies in the middle ear cavity and seats around the round window. The presence of the double bend and the location of the opening within the middle ear, however, prevent the device from functioning as a drainage conduit. The article further relates that 20 of 40 tamponades utilizing the device required a mucous membrane implantation and 8 of the devices in those cases were obstructed.
Silicone rubber tubing, such as that marketed by Dow Corning under the trademark Silastic is used for many of the previously-described devices. Silastic tubing is generally acknowledged to be compatible with body tissue and therefore suitable as a prosthetic implant. Silastic material is also used for breast implantations, to drain areas of the brain, and in other surgical applications. Flanged tubes of other materials are also used in surgical procedures.
The primary requirements for a ventilation restoring procedure and prosthesis are that the technique involve minimal technical difficulties and a negligible risk of complications and that the device provide adequate and permanent ventilation and drainage. In addition, the tympanic membrane should remain intact and there should be no increased risk of middle ear infection. Further, the procedure preferably is applicable to children and adults and should not result in permanent discomfort for the patient.